posix/execvpe.c

   1 /* Copyright (C) 1991-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <unistd.h>
  19 #include <stdarg.h>
  20 #include <stdbool.h>
  21 #include <stdlib.h>
  22 #include <string.h>
  23 #include <errno.h>
  24 #include <paths.h>
  25 #include <confstr.h>
  26 #include <sys/param.h>
  27
  28 #ifndef PATH_MAX
  29 # ifdef MAXPATHLEN
  30 #  define PATH_MAX MAXPATHLEN
  31 # else
  32 #  define PATH_MAX 1024
  33 # endif
  34 #endif
  35
  36 /* The file is accessible but it is not an executable file.  Invoke
  37    the shell to interpret it as a script.  */
  38 static void
  39 maybe_script_execute (const char *file, char *const argv[], char *const envp[])
  40 {
  41   ptrdiff_t argc;
  42   for (argc = 0; argv[argc] != NULL; argc++)
  43     {
  44       if (argc == INT_MAX - 1)
  45         {
  46           errno = E2BIG;
  47           return;
  48         }
  49     }
  50
  51   /* Construct an argument list for the shell based on original arguments:
  52      1. Empty list (argv = { NULL }, argc = 1 }: new argv will contain 3
  53         arguments - default shell, script to execute, and ending NULL.
  54      2. Non empty argument list (argc = { ..., NULL }, argc > 1}: new argv
  55         will contain also the default shell and the script to execute.  It
  56         will also skip the script name in arguments and only copy script
  57         arguments.  */
  58   char *new_argv[argc > 1 ? 2 + argc : 3];
  59   new_argv[0] = (char *) _PATH_BSHELL;
  60   new_argv[1] = (char *) file;
  61   if (argc > 1)
  62     memcpy (new_argv + 2, argv + 1, argc * sizeof(char *));
  63   else
  64     new_argv[2] = NULL;
  65
  66   /* Execute the shell.  */
  67   __execve (new_argv[0], new_argv, envp);
  68 }
  69
  70
  71 /* Execute FILE, searching in the `PATH' environment variable if it contains
  72    no slashes, with arguments ARGV and environment from ENVP.  */
  73 int
  74 __execvpe (const char *file, char *const argv[], char *const envp[])
  75 {
  76   /* We check the simple case first. */
  77   if (*file == '\0')
  78     {
  79       __set_errno (ENOENT);
  80       return -1;
  81     }
  82
  83   /* Don't search when it contains a slash.  */
  84   if (strchr (file, '/') != NULL)
  85     {
  86       __execve (file, argv, envp);
  87
  88       if (errno == ENOEXEC)
  89         maybe_script_execute (file, argv, envp);
  90
  91       return -1;
  92     }
  93
  94   const char *path = getenv ("PATH");
  95   if (!path)
  96     path = CS_PATH;
  97   /* Although GLIBC does not enforce NAME_MAX, we set it as the maximum
  98      size to avoid unbounded stack allocation.  Same applies for
  99      PATH_MAX.  */
 100   size_t file_len = __strnlen (file, NAME_MAX) + 1;
 101   size_t path_len = __strnlen (path, PATH_MAX - 1) + 1;
 102
 103   /* NAME_MAX does not include the terminating null character.  */
 104   if ((file_len - 1 > NAME_MAX)
 105       || !__libc_alloca_cutoff (path_len + file_len + 1))
 106     {
 107       errno = ENAMETOOLONG;
 108       return -1;
 109     }
 110
 111   const char *subp;
 112   bool got_eacces = false;
 113   /* The resulting string maximum size would be potentially a entry
 114      in PATH plus '/' (path_len + 1) and then the the resulting file name
 115      plus '\0' (file_len since it already accounts for the '\0').  */
 116   char buffer[path_len + file_len + 1];
 117   for (const char *p = path; ; p = subp)
 118     {
 119       subp = __strchrnul (p, ':');
 120
 121       /* PATH is larger than PATH_MAX and thus potentially larger than
 122          the stack allocation.  */
 123       if (subp - p >= path_len)
 124         {
 125           /* If there is only one path, bail out.  */
 126           if (*subp == '\0')
 127             break;
 128           /* Otherwise skip to next one.  */
 129           continue;
 130         }
 131
 132       /* Use the current path entry, plus a '/' if nonempty, plus the file to
 133          execute.  */
 134       char *pend = mempcpy (buffer, p, subp - p);
 135       *pend = '/';
 136       memcpy (pend + (p < subp), file, file_len);
 137
 138       __execve (buffer, argv, envp);
 139
 140       if (errno == ENOEXEC)
 141         /* This has O(P*C) behavior, where P is the length of the path and C
 142            is the argument count.  A better strategy would be allocate the
 143            substitute argv and reuse it each time through the loop (so it
 144            behaves as O(P+C) instead.  */
 145         maybe_script_execute (buffer, argv, envp);
 146
 147       switch (errno)
 148         {
 149           case EACCES:
 150           /* Record that we got a 'Permission denied' error.  If we end
 151              up finding no executable we can use, we want to diagnose
 152              that we did find one but were denied access.  */
 153             got_eacces = true;
 154           case ENOENT:
 155           case ESTALE:
 156           case ENOTDIR:
 157           /* Those errors indicate the file is missing or not executable
 158              by us, in which case we want to just try the next path
 159              directory.  */
 160           case ENODEV:
 161           case ETIMEDOUT:
 162           /* Some strange filesystems like AFS return even
 163              stranger error numbers.  They cannot reasonably mean
 164              anything else so ignore those, too.  */
 165             break;
 166
 167           default:
 168           /* Some other error means we found an executable file, but
 169              something went wrong executing it; return the error to our
 170              caller.  */
 171             return -1;
 172         }
 173
 174       if (*subp++ == '\0')
 175         break;
 176     }
 177
 178   /* We tried every element and none of them worked.  */
 179   if (got_eacces)
 180     /* At least one failure was due to permissions, so report that
 181        error.  */
 182     __set_errno (EACCES);
 183
 184   return -1;
 185 }
 186
 187 weak_alias (__execvpe, execvpe)